A number of metalloproteins containing nonheme-iron centers have been investigated in the past decade. This class includes catechol 2,3-dioxygenase (2,3-CTD), purple acid phosphatase, methane monooxygenase, and stearoyl desaturase. We have obtained and analyzed data for 2,3-CTD and its substrate complexes. A 5-coordinate iron site with an average Fe-ligand distance of 2.09 is found in the isolated protein; catechol binding elicits a new short bond at 1.93, which is proposed to be the oxygen from the deprotonated hydroxyl group of the coordinated catecholate monoanion. This paper is published. We have collected and analyzed data on an Fe (III) Zn(II) derivative of the purple acid phosphatase from porcine uterus which allows us to look at the Fe(III) and the Zn (II) sites separately. In the phosphate complex of this derivative, the observation of Fe-Zn and M-P (M=3D Fe, Zn) distances of 3.3 and 3.2, respectively, indicates an FeZn(OR)2 core structure and phosphate is proposed to bind to the metal center in a bridging mode. This paper is submitted. Data was also collected on methane monooxygenase hydroxylase (MMOH) and stearoyl ACP = C69 desaturase, the newest member of this class of proteins. XAS analysis of MMOH suggests the presence of two Fe-Fe distances of about 3 and 3.4, which are proposed to reflect two populations of MMOH molecules with either a bis(m-hydroxo)(m-carboxylato)-or a (m-hydroxox)(m-carboxylato)diiron(III) core structure, respectively. The paper is in press. With the crystallographic data available for hemerythrin, ribonucleotide reductase and the hydroxylase component of methane monooxygenase, kidney bean phosphatase, and EXAFS data for the other proteins, we will be able to identify the common structural features that make up these dimetallic sites within this class and to discern the variations in structure that control mechanism and function. We have also examined the EXAFS of model complexes related to intermediates of these iron proteins; these results are published. Data was also taken and analyzed on copper model complexes modeling the copper dioxygen chemistry in metalloproteins, and this paper is published. In two cases, the EXAFS analysis has been crucial for the structure determination of these unstable model complexes.